This invention relates to a torque motor and, more particularly to a torque motor which may be used as an actuator for a throttle apparatus of an internal combustion engine and the like.
As disclosed in JP-A 3-31529, a conventional torque motor has a rotor, a stator and a solenoid coil. The rotor includes permanent magnets shaped arcuately as a part of the rotor. The stator is made of magnetic substance to surround the rotor. The solenoid coil generates magnetic pole of the stator when it is energized. The rotor is rotatably actuated when the magnetic pole of the stator attracts a magnetic pole of the rotor, and such conventional torque motor may be used as an actuator for a throttle valve apparatus for an internal combustion engine.
It is proposed that a torque motor uses a plurality of plate-shaped permanent magnets on its outer periphery. In other words, a torque motor has a rotor comprising a rotor core and two permanent magnet groups arranged 180.degree. oppositely to each other, that is, symmetrically with respect to a rotary axis of the rotor. The permanent magnet groups are spaced apart from each other on the rotor core in the circumferential direction. The magnet group has a plurality of plate-shaped permanent magnets arranged in the circumferential direction on a part of the outer periphery of the rotor core, while the other magnet group has the same number of plate-shaped permanent magnets arranged in the similar manner on another part of the rotor core. The stator cores are joined at a pair of stator core connecting parts. The connecting parts for the corresponding magnet groups are provided 180.degree. oppositely to each other on the circumference of the rotor core. The rotor is held rotatably inside of a pair of stator cores between which solenoid units are sandwiched.
The above torque motor generates a torque varying in dependence on the rotational angle of the rotor. In other words, generated torque is reduced in certain range of rotational angle of the rotor.